In recent years, a low-quality aggregate that has not been actively used as a concrete material has been increasingly used with depletion of a good-quality fine aggregate such as river sand. In a hydraulic composition using the low-quality fine aggregate, the viscosity in a fresh state is high even at a general water powder ratio (W/B), and the workability tends to be decreased. Such problems are likely to occur when the content of impurities (e.g., clay) contained in the aggregate is particularly large.
Further, an aggregate used as a material for the hydraulic composition is a natural product, and thus the content of impurities varies. When a conventional polycarboxylic acid-based dispersant is used, the amount of the dispersant that is necessary for obtaining constant flowability varies depending on the kind and derivation of used aggregate, and the like. Therefore, in the actual production of the hydraulic composition, it is necessary to adjust the amount of the dispersant used during using. Accordingly, the operation is complicated in various terms. When a large amount of the low-quality aggregate is used, it is often necessary that the amount of the dispersant added be increased to secure constant flowability. This causes an increase in production cost.
Some examples of the prior art to solve the problems are disclosed. The examples include a method for using the conventional polycarboxylic acid-based dispersant in combination with another component and a method for optimizing the structure of the polycarboxylic acid-based dispersant itself. By the methods, the flowability is improved and the effectiveness as a polycarboxylic acid-based water reducing agent is enhanced.
As one example of the method for using the other component in combination, proposed is the use of a substance containing an inorganic cation (e.g., calcium nitrate), a substance containing an organic cation (e.g., tetrabutylammonium bromide), and a polar organic molecule (e.g., polyethylene glycol and sodium hexametaphosphate) as clay activity-modifying substances in combination with an EO/PO plasticizer (i.e., polycarboxylic acid-based water reducing agent) during use of a low-quality aggregate containing a swellable clay (e.g., smectite and montmorillonite) (Patent Document 1). Thus, the effectiveness of the polycarboxylic acid-based water reducing agent is improved. Further, proposed is the use of a cationic polymer containing a quaternary nitrogen (e.g., poly(diallyldimethylammonium) salt) in combination with a high-performance water reducing agent or a high-performance AE water reducing agent (polycarboxylic acid-based water reducing agent) during use of a low-quality fine aggregate (Patent Document 2). Thus, the fresh state of concrete viscosity, flow retention, and the like is improved. Moreover, proposed is the use of a polycationic compound (e.g., polydiallyldimethylammonium chloride) and a polyhydroxyl or hydroxyl carboxylate component (e.g., sodium gluconate) in combination with a polycarboxylate-based dispersant during use of a clay-containing aggregate (Patent Document 3). The dispersant improves the maintenance of dose efficiency exhibited in cement mortar.
As one example of the method for improving the structure of the polycarboxylic acid-based dispersant itself, the use of a comb copolymer containing a main hydrocarbon chain and a side chain containing a gem-bisphosphonate group in addition to a carboxy group and a polyoxyalkylene group as a superplasticizer for a suspended substance of mineral particles is proposed (Patent Document 4). Thus, the flowability of the suspended substance is improved.